The present invention relates to a novel catalyst carrier comprising gamma alumina and method of manufacture of same.
It is well-known that gamma alumina particles which serve as a carrier substance of a catalyst composition can be manufactured by the oil-drop method utilizing alumina hydrosol or extrusion of gamma alumina powder. When comparing the oil dropped gamma alumina with the extruded gamma alumina, it may generally be said that the former is superior in physical strength, in particular, a low attrition loss, but it is low in apparent bulk density, while the latter is relatively high in apparent bulk density but it exhibits a considerably heavy attrition loss. Therefore, it is extremely importance to obtain gamma alumina having a high apparent bulk density by the oil-drop method.
A process of manufacturing spherical alumina is taught in U.S. Pat. No. 2,620,314. According thereto, spherical alumina is manufactured by the steps of commingling alumina hydrosol with a gelling agent which is hydrolyzable at an elevated temperature, dispersing the resulting mixture as droplets in a suspending medium thereby forming hydrogel particles, ageing the thus obtained hydrogel particles, washing with water, drying and calcining.
In the case of manufacturing spherical alumina by means of the oil-drop method, the apparent bulk density thereof may be increased or decreased to some extent by controlling the conditions for ageing the hydrogel particles, more particularly the ammonia concentration and temperature in the ammonia ageing step, but in order to manufacture higher apparent bulk density spherical alumina it is required that the weight ratio of aluminum to chloride should be lowered in the alumina hydrosol, per se, that is, the precursor of said spherical alumina.
In the case of the conventional alumina hydrosol employed in the oil-drop method, however, the weight ratio of aluminum to chloride is about 1.0 at the lowest, and an alumina hydrosol having a weight ratio lower than that, even if applied to the oil-drop method, can produce no satisfactory spherical alumina. The reasons therefor may be enumerated as follows. The first reason is that in the conventional method it is difficult to manufacture a uniform alumina hydrosol having a weight ratio of aluminum to chloride of less than 1.0. And the second reason is that it is difficult to make a mixture comprising such a uniform alumina hydrosol whose weight ratio of aluminum to chloride is 1 or less and a gelling agent such as hexamethylenetetramine or the like fulfill the necessary conditions suitable for the oil-drop method.
In this connection, the properties of the conventional gamma alumina manufactured by the oil-drop method are as shown in Table-1.
TABLE-1 ______________________________________ Apparent bulk density (g/cc) 0.30-0.64 Total pore volume (cc/g) 0.55-0.65 Content of micro pore having a diameter of 60-110A in total pore volume (%) 70 or less Surface area (m.sup.2 /g) 210 or less Average crushing strength (Kg) 8 or less Attrition loss* (wt. %) 0.2 ______________________________________ *denotes the percentage by weight of carrier substances powdered by placing carrier substances in the sample container of a vibrating blender mill and vibrationtreating them at 3000 vibrations per minutes for 20 minutes.
To meet the demand for spherical alumina of high apparent bulk density, large surface area and improved physical strength such as crushing strength, attrition loss and so forth, we have carried out a series of investigations for the purpose of solving the aforesaid two problems to thereby develope a method of manufacturing spherical alumina of high apparent bulk density and further improved physical properties by means of the oil-drop method in the manner of exerting our ingenuity in the preparation of the alumina hydrosol as well as specifying the mixing ratio of the alumina hydrosol whose weight ratio of aluminum to chloride is 1 or less and a gelling agent and the concentration of aluminum in the resulting mixture.